Excess hair growth in a spot on the back over the spine is known as faun tail

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Faun Tail

Hypertrichosis may be generalized or localized and each of these hypertrichosis may be either acquired or congenital. Faun tail is localized congenital hypertrichosis. Hypertrichosis of this type is of utmost concern when it is a sign of underlying occult neural abnormalities as is frequently the case with mid line hair on the back.

Excess hair on the spine is frequently a marker for underlying spinal dysraphisms such as dermal cyst or sinus, myelomeninggocele, diastematomyelia, vertebral abnormalities or a subdural or extradural lipoma. The term spinal dysraphisms is used to denote those abnormalities involving any or all of the middle tissues of the back. Spinal hypertrichosis, seen as a discrete patch of sacral terminal hair growth over the lower back is termed a ‘faun tail’. If the hypertrichosis is seen as a midline vellus hair growth, it is termed “silky down”.

The separation of the neuroectoderm from the epithelial ectoderm occurs in the third to fifth week of pregnancy and is initiated along the mid-line posteriorly. The cleavage can be incomplete at any phase, so that a defect may appear in the skin, vertebrae, spinal cord, and/or central nervous system.

A faun tail is frequently associated with one of several underlying spinal defects including spina bifida occulta which is vertebral defect without exposure of neural tissues, spima bifida, traction bands and diastematomyelia. Fibrous bands may tie the spinal cord or cauda equine to bone or skin directly or through attachment to the meninges or through a tight filum terminale. A meningocele manqué refers to aberrant nerve roots, fibrous bands and adhesions that tether the spinal cord, nerve roots and filum terminale within the meninges and may continue through the dura to the skin. 24 percent of such cases have overlying hypertrichosis.

Diastematomyelia is duplication or splitting of a portion of the spinal cord through a bony spur or fibrous passes and attaches to the vertebral body anteriorly and /or to the neural posteriorly. More than 40 percent of persons with diastematomyelia have patches of hair overlying the neural-bony abnormality. These abnormalities may not cause neurologic problems in infancy but symptoms do eventually appear from childhood to early adulthood. Symptoms appear because there is a normally occurring dissimilar growth of the spinal cord ascending in the vertebral column over the first five years of life. The traction on the cord either directly or by the cord being hung up by either the bony or the fibrous spur in diastematommyelia will eventually cause a neurologic deficit. Recognition of the process will allow prophylactic surgery.

Faun tails are usually evident by early infancy and appear more frequently in females than in males. It should be noted, however, that the hair may not be at the level of the neural defect itself but will be at the general region. Midback hypertrichosis is most common in the sacral or lumbar region and less frequently as one moves cephalad.

Midback hypertrichosis may accompany other cutaneous abnormalities that also signal underlying neurocutaneous abnormalities or that may secondarily cause damage to underlying neurologic structures. Dermal sinuses, usually 1 mm to 2 mm in diameter and close to or at the dorsal midline are often associated with local pigmentation, port wine discoloration, or protrusion of the hair from the sinus. These sinuses can extend into the spinal canal and serve as an entry for infections or can expand into an epidermis or dermoid cyst. This can lead to neurologic deficits secondary to pressure on the cord with tumor growth. Midline lipomas are frequently attached to the cord or cauda equine, filum terminale and onus medullaris. Excision or manipulation may lead to meningitis or central nervous system infection.

Midline dorsal patches of hypertrichosis should lead one to look for neurologic deficits and underlying bony abnormalities. The absence of neurologic deficit at the time of examination does not rule out an underlying neurologic abnormality. Invasive procedures as mylography are potential sources of infection and should be avoided if non-invasive techniques such as magnetic resonance imaging are available. Manipulation or excision of midline dorsal cutaneous structures should not be done without a thorough examination of the underlying cord and spinal column and without prior neurosurgical consultations.

Magnetic resonance imaging evaluation of the spinal hypertrichosis is important because early surgical intervention may prevent neurologic damage.

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